Electroplating contacts with silver-alloys in a basic bath

ABSTRACT

A method for silver-alloy plating an electrical contact and a silver-alloy plated electrical contact are provided. The method includes cleaning the electrical contact by removing contaminates and exposing the electrical contact to at least one of an acid or base. The method includes preparing a sliver-alloy plating bath including water, a silver complex, and a metal complex, the metal complex being at least one of nickel or cobalt. The method includes silver-alloy plating the electrical contact in the silver-alloy plating bath, wherein the plating bath has a pH of greater than 7. The metal complex forms about 0.3% to about 50% by weight of a content of a silver-alloy plated deposit.

FIELD OF THE INVENTION

The subject matter described herein generally relates to silver platedelectrical contacts and more specifically silver-alloy plated electricalcontacts in a basic electroplating bath.

BACKGROUND OF THE INVENTION

Electrical connectors include electrical contacts that are frequentlyplated with a metal compound to improve various properties of theelectrical contact. For example, plating the contact may improve acoefficient of friction of the contact. As such, less force is requiredto insert the contact into a corresponding contact. Accordingly, damageto the electrical contact may be avoided. Additionally, plating theelectrical contact may improve a durability of the contact therebyreducing wear on the electrical contact and enabling the electricalcontact to be used in harsh environments. Moreover, plating the contactmay reduce electromigration and tarnishing of the electrical contact.

Typically, electrical contacts are plated with gold. Gold is generallydurable and provides a low coefficient of friction, and a low levelcontact resistance. However gold increases the costs associated withplating the electrical contact. As an alternative to gold, electricalcontacts may be plated with silver, which is generally cheaper thangold. However, silver is much softer than gold and provides lessdurability than gold. Additionally, silver has a high coefficient offriction and is subject to electromigration and tarnishing.

Silver-alloy plated contacts that do not suffer from one or more of theabove drawbacks would be desirable in the art.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment, a method for silver-alloy plating anelectrical contact is provided. The method includes cleaning theelectrical contact by removing contaminates and exposing the electricalcontact to at least one of an acid or base. The method includespreparing a sliver-alloy plating bath including water, a silver complex,and a metal complex, the metal complex being at least one of nickel orcobalt. The method includes silver-alloy plating the electrical contactin the silver-alloy plating bath, wherein the plating bath has a pH ofgreater than 7.

In another exemplary embodiment, a silver-alloy plated electricalcontact is provided. The silver-alloy plated electrical contact isformed in a silver-alloy plating bath having a silver complex, a metalcomplex including at least one of nickel or cobalt. The metal complexforms about 0.3-50% by weight of a content of a silver-alloy plateddeposit.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a connector formed in accordance with anexemplary embodiment.

FIG. 2 is flowchart of a method for silver-alloy plating an electricalcontact in accordance with an embodiment.

FIG. 3 is a flowchart of a method for silver-alloy plating an electricalcontact in accordance with another embodiment.

FIG. 4 is a microscopic photograph of a silver-alloy plating on anelectrical contact in accordance with an embodiment of the presentdisclosure using silver thiosulfate.

FIG. 5 is a microscopic photograph of a silver-alloy plating on anelectrical contact in accordance with an embodiment of the presentdisclosure using silver succinimide.

Wherever possible, the same reference numbers will be used throughoutthe drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION

Provided is an exemplary silver-alloy plated contact and a process ofmanufacturing a silver-alloy plated contact. Embodiments of the presentdisclosure, for example, in comparison to plated contacts and processesof manufacturing plated contacts that do not include one or more of thefeatures disclosed herein, reduce or eliminate corrosion, reduce oreliminate delamination, provides harder silver deposits, reducecoefficient of friction, and improve wear durability.

FIG. 1 is a perspective view of a connector 50 formed in accordance withan embodiment. The connector 50 includes a body 52 having a plurality ofcavities 54. Electrical contacts 56 are inserted into the cavities 54.The contacts 56 are high-reliability contacts that have been stamped andformed. The contacts 56 are formed for use in applications that requirecontact durability, for example, military, aircraft, satellite, missileapplications, automotive, communications or the like. The contacts 56are configured to withstand high temperatures, high amounts of shock andvibration, and the like. The contacts 56 are formed from a conductivematerial, for example, copper. After forming the contacts 56, at least aportion of each contact 56 is covered with a hard silver-alloy platinglayer to inhibit corrosion, reduce coefficient of friction, reducecontact resistance, and increase durability.

In an exemplary embodiment, the silver plated electrical contact 56 isformed in a silver-alloy plating bath having a molar concentration of asilver complex of about 0.01M to about 0.5M and a molar concentration ofa metal complex of about 0.01M to about 0.5M. The silver complex may beat least one of silver thiosulfate or silver succinimide and may formabout 55 percent to about 99.7 percent by weight, or alternatively about90 percent to about 99.7 percent by weight, or alternatively about 95percent to about 99.7 percent by weight of a content in a resultingsilver-alloy deposit on a contact. The metal complex may be at least oneof nickel or cobalt and may form about 0.3 percent to about 50 percentby weight, or alternatively about 0.3 percent to about 10 percent byweight, or alternatively about 0.3 percent to about 5 percent by weightof a content in a resulting silver-alloy deposit on contact 56. In oneembodiment, the silver-alloy plated electrical contact 56 has a grainsize of silver that is sub-micron, as shown in FIGS. 4 and 5. Thecontact 56 may include nickel plating that is plated on the contact 56before the contact 56 is formed in the silver-alloy plating bath.Moreover, the contact 56 may include a silver, gold or palladium strikeplating that is formed on the contact 56 after the contact 56 is nickelplated and before the contact 56 is silver-alloy plated. In oneembodiment, the silver-alloy plating bath also includes at least onebrightener of an amine group additive or polyethyleneimine (PEI). Othersuitable examples of brighteners include, but are not limited to,thiourea, polyethylene glycol, sodium saccharin, and 2-Butyne-1,4-diol.For example, the silver plating bath may have a concentration of PEI ofapproximately 2000 parts per million or less. In another embodiment,silver plating bath may have a concentration of sodium saccharin of 1g/L or less or alternatively a concentration of 2-Butyne-1,4-diol of 1g/L or less.

It should be noted that the connector 50 and the electrical contacts 56shown in FIG. 1 are exemplary only. The various embodiments andprocesses described herein may be utilized with any suitable connectorand/or electrical contact.

FIG. 2 is a flowchart of a method 100 for silver plating an electricalcontact in accordance with an embodiment. At 102, an electrical contactis formed. The electrical contact may be any suitable contact fortransmitting electrical signals. The electrical contact may be made fromany suitable conductive material, for example, copper or a copper alloy.The electrical contact may be a stamped and formed contact.Alternatively, the electrical contact may be formed using an appropriatedie. The electrical contact is configured to have at least a portionthereof silver-alloy plated. For example, a mating end of the electricalcontact may be configured for silver-alloy plating. Optionally, theentire electrical contact may be configured for silver-alloy plating.

At 104, the electrical contact is degreased. During degreasing, achemical may be used to remove oils, such as machining fluids, or othercontaminants from the electrical contact. For example, the electricalcontact may be degreased using petroleum, chlorine, or alcohol basedsolvents to dissolve the machining fluids and other contaminants. At106, the electrical contact is rinsed to remove any degreasing chemicalstherefrom. For example, the electrical contact may be rinsed with water.

At 108, the electrical contact undergoes acid activation. The acidactivation may be performed with a series of at least one of acids orbases to remove unwanted contaminants from a surface of the electricalcontact to reduce poor plating. Additionally, the acid activation may beperformed with a weak acid etch or with a proprietary solution. At 110,the electrical contact is rinsed again.

At 112, a sliver-alloy plating process is performed. The silver-alloyplating process includes preparing a silver-alloy plating bath. In anexemplary embodiment, an aqueous silver-alloy plating bath is formedhaving deionized water, a silver complex, and a metal complex. Forexample, the silver for the silver complex may be provided as silvernitrate. In one embodiment, the silver-alloy plating bath includes about1.7 gram/Liter (g/L) to about 17 g/L of silver as silver nitrate andabout 6 g/L to about 63 g/L of sodium thiosulfate to form the silvercomplex as a silver thiosulfate. In one embodiment, a sodiummetabisulfite is added as a supporting electrolyte to the silver complexat a concentration of about 1.9 g/L to about 19 g/L. In anotherembodiment, the silver-alloy plating bath includes about 1 g/L to about5 g/L of silver as silver nitrate and about 10 g/L to about 20 g/L ofsuccinimide to form the silver complex as silver succinimide. The silvercomplex is at a molar concentration of about 0.01M to about 0.5M oralternatively about 0.01M to about 0.1M in the silver-alloy platingbath.

The metal complex may be provided as a nickel compound or cobaltcompound, such as nickel sulfate or nickel sulfamate or cobalt sulfateor cobalt sulfamate. In one embodiment, the silver-alloy plating bathincludes about 15.7 g/L to about 77 g/L of nickel as nickel sulfate ornickel sulfamate and about 25.8 g/L to about 130 g/L sodium citrate andabout 5 g/L to about 35 g/L of ammonia hydroxide to form the metalcomplex as nickel citrate-ammonia. In one embodiment, the metal complexmay be a cobalt compound, such as cobalt sulfate or cobalt sulfamate.For example, the silver-alloy plating bath may include about 15.7 g/L toabout 77 g/L of cobalt as cobalt sulfate and about 25.8 g/L to about 130g/L sodium citrate and about 5 g/L to about 35 g/L of ammonia hydroxideto form the metal complex as cobalt citrate-ammonia. The metal complexis at a molar concentration of about 0.01M to about 0.5M oralternatively about 0.01M to about 0.1M in the silver-alloy platingbath. The molar ratio of metal complex to silver complex is from about20:1 to about 1:1 or alternatively about 10:1 to about 5:1. The metalcomplex forms about 0.3% to about 50% by weight of a content of asilver-alloy plated deposit

The pH of the silver-alloy plating is preferably greater than 7. The pHof the silver-alloy plating bath may be adjusted to about 7 to about 11,or alternatively about 8 to about 10, or alternatively about 8 to about9, using ammonia hydroxide. The silver-alloy plating process alsoincludes silver-alloy plating the electrical contact in the silver-alloyplating bath. The silver-alloy plating process can be performed in aconventional high-speed, spot, or jet plating process. The silver-alloyplating process may be performed at room temperature or in thetemperature range of about 20° C. to about 50° C. The silver-alloyplating process may be performed at a cathode current density of about 5ampere:/square foot (A/ft² or ASF) to about 40 A/ft².

In one embodiment, polyethyleneimine (PEI), with a molecular weight ofapproximately 500-2000 grams per mole, may be added to the silver-alloyplating bath at concentration of 1000 parts per million. The addition ofPEI may result in a silver-alloy plating deposit having crystallinestructure at a sub-micron size range and a lower coefficient offriction. Alternatively, brighteners such as thiourea, polyethyleneglycol, sodium saccharin, and 2-Butyne-1,4-diol may be added. Thebrighteners may be added to the silver-alloy plating bath at a targetedconcentration of approximately 1 g/L or less.

After the silver plating process, the electrical contact is rinsed, at114. At 116, the electrical contact is dried. Optionally, the electricalcontact may be baked. In one embodiment, the electrical contact may beannealed. For example, the electrical contact may be annealed at 125° C.for 100 hours.

FIG. 3 is a flowchart of a method 200 for silver plating an electricalcontact in accordance with another embodiment. At 202 an electricalcontact is formed. The electrical contact may be formed as set forth inthe method 100 shown in FIG. 2. At 204, the electrical contact isdegreased and, at 206, the electrical contact is rinsed to remove anydegreasing chemicals therefrom. The electrical contact may be degreasedand rinsed as set forth in the method 100 shown in FIG. 2. At 208, theelectrical contact undergoes acid activation and, at 210, the electricalcontact is rinsed again. The electrical contact may undergo acidactivation and be rinsed as set forth in the method 100 shown in FIG. 2.

At 212, the electrical contact undergoes nickel plating. In oneembodiment, the electrical contact may be nickel plated usingelectroplating. Alternatively, the electrical contact may be nickelplated using electroless nickel plating. The nickel plating layersprovide additional strength and durability to the electrical contact.The nickel plating process may be performed with nickel and/or nickelalloys. The nickel plating process may also improve a corrosionresistance of the electrical contact. After nickel plating, theelectrical contact is rinsed, at 214, as described in method 100 shownin FIG. 2.

At 216, the electrical contact undergoes silver strike plating. Strikeplating forms a thin layer of silver plating on the electrical contact.For example, the strike plating layer may be less than approximately 0.1micrometer thick. The strike plating layer may provide additionaladherence to the electrical contact. Accordingly, the strike platinglayer may serve as a foundation for subsequent plating processes. In anexemplary embodiment, the strike plating layer forms a foundation for asilver plating layer. After the silver strike plating process, theelectrical contact is rinsed, at 218.

At 220, a sliver-alloy plating process is performed. The silver-alloyplating process includes preparing a silver-alloy plating bath. In anexemplary embodiment, an aqueous silver-alloy plating bath is formedhaving deionized water, a silver complex, and a metal complex. Forexample, the silver for the silver complex may be provided as silvernitrate. In one embodiment, the silver-alloy plating bath includes about1.7 gram/Liter (g/L) to about 17 g/L of silver as silver nitrate andabout 6 g/L to about 63 g/L of sodium thiosulfate to form the silvercomplex as a silver thiosulfate. In one embodiment, a sodiummetabisulfite is added as a supporting electrolyte to the silver complexat a concentration of about 1.9 g/L to about 19 g/L. In anotherembodiment, the silver-alloy plating bath includes about 1 g/L to about5 g/L of silver as silver nitrate and about 10 g/L to about 20 g/L ofsuccinimide to form the silver complex as silver succinimide. The silvercomplex is at a molar concentration of about 0.01M to about 0.5M oralternatively about 0.01M to about 0.1M in the silver-alloy platingbath.

The metal complex may be provided as a nickel compound or cobaltcompound, such as nickel sulfate or nickel sulfamate or cobalt sulfateor cobalt sulfamate. In one embodiment, the silver-alloy plating bathincludes about 15.7 g/L to about 77 g/L of nickel as nickel sulfate ornickel sulfamate and about 25.8 g/L to about 130 g/L sodium citrate andabout 5 g/L to about 35 g/L of ammonia hydroxide to form the metalcomplex as nickel citrate-ammonia. In one embodiment, the silver-alloyplating bath may include about 15.7 g/L to about 77 g/L of cobalt ascobalt sulfate or cobalt sulfamate and about 25.8 g/L to about 130 g/Lsodium citrate and about 5 g/L to about 35 g/L of ammonia hydroxide toform the metal complex as cobalt citrate-ammonia. The metal complex isat a molar concentration of about 0.01M to about 0.5M or alternativelyabout 0.01M to about 0.1M in the silver-alloy plating bath. The molarratio of metal complex to silver complex is from about 20:1 to about1:1, or alternatively about 10:1 to about 1:1, or alternatively about10:1 to about 5:1. The metal complex forms about 0.3% to about 50% byweight of a content of a silver-alloy plated deposit for a silver-alloyplated electrical contact.

The pH of the silver-alloy plating is preferably greater than 7. The pHof the silver-alloy plating bath may be adjusted to about 7 to about 11,or alternatively about 8 to about 10, or alternatively about 8 to about9, using ammonia hydroxide. The silver-alloy plating process alsoincludes silver-alloy plating the electrical contact in the silver-alloyplating bath. The silver-alloy plating process can be performed in aconventional high-speed, spot, or jet plating process. The silver-alloyplating process may be performed at room temperature or in thetemperature range of about 20° C. to about 50° C. The silver-alloyplating process may be performed at a cathode current density of about 5ampere/square foot (A/ft² or ASF) to about 40 A/ft².

In one embodiment, polyethyleneimine (PEI), with a molecular weight ofapproximately 500-2000 grams per mole, may be added to the silver-alloyplating bath at concentration of 1000 parts per million. The addition ofPEI may result in a silver-alloy plating deposit having crystallinestructure at a sub-micron size range and a lower coefficient offriction. Alternatively, brighteners such as thiourea, polyethyleneglycol, sodium saccharin, and 2-butyne-1,4-diol may be added. Thebrighteners may be added to the silver-alloy plating bath at a targetedconcentration of approximately 1 g/L or less.

After the silver plating process, the electrical contact is rinsed, at222. At 224, the electrical contact is dried. Optionally, the electricalcontact may be baked. In one embodiment, the electrical contact may beannealed. For example, the electrical contact may be annealed at 125° C.for 100 hours.

FIG. 4 is a microscopic picture of the surface of a silver-alloy platedcontact according to an embodiment of this disclosure. The silvercomplex used was silver thiosulfate and the metal complex used wasnickel citrate-ammonia. The larger grains, labeled 400, aresilver-nickel alloy and the smaller grains, labeled 402, aresilver-nickel alloy. Using the procedure in the present disclosureallows for control of the nickel content in the deposit. Thesilver-nickel alloy grains 400 and 402 indicate that a higher hardnessand great wear performance will be obtained from the coating.

FIG. 5 is a microscopic picture of the surface of a silver-alloy platedcontact according to an embodiment of this disclosure. The silvercomplex used was silver succinimide and the metal complex used wasnickel citrate-ammonia. The larger grains, labeled 500, aresilver-nickel alloy and the smaller grains, labeled 502, aresilver-nickel alloy. Using the procedure in the present disclosureallows for control of the nickel content in the deposit. Thesilver-nickel alloy grains 500 and 502 indicate that a higher hardnessand great wear performance will be obtained from the coating.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method for silver-alloy plating an electricalcontact comprising: cleaning the electrical contact by removingcontaminates and exposing the electrical contact to at least one of anacid or base; preparing a sliver-alloy plating bath including water, asilver complex, and a metal complex, the metal complex being at leastone of nickel or cobalt; and silver-alloy plating the electrical contactin the silver-alloy plating bath, wherein the plating bath has a pH ofgreater than
 7. 2. The method of claim 1, wherein the pH of the platingbath is about 7 to about
 11. 3. The method of claim 1, wherein the metalcomplex is nickel citrate-ammonia.
 4. The method of claim 1, wherein themetal complex is cobalt citrate-ammonia.
 5. The method of claim 1,wherein the silver complex is silver thiosulfate.
 6. The method of claim1, wherein the silver complex is silver succinimide.
 7. The method ofclaim 1, wherein the silver complex is at a molar concentration of about0.01M to about 0.5M.
 8. The method of claim 7, wherein the silvercomplex is at a molar concentration of about 0.01M to about 0.1M.
 9. Themethod of claim 1, wherein the metal complex is at a molar concentrationof about 0.1M to about 0.5M.
 10. The method of claim 1, wherein themolar ratio of metal complex to silver complex is from about 10:1 toabout 1:1.
 11. The method of claim 4, wherein a silver deposit on theelectrical contact is about 55% to about 99% weight percent and a nickeldeposit is the balance.
 12. The method of claim 5, wherein a silverdeposit on the electrical contact is about 90% to about 99% weightpercent and a nickel deposit is the balance.
 13. The method of claim 1,wherein the silver-alloy plating bath further includes brighteners. 14.A silver-alloy plated electrical contact formed in a silver-alloyplating bath having a silver complex, a metal complex including at leastone of nickel or cobalt, wherein the metal complex forms about 0.3% toabout 50% by weight of a content of a silver-alloy plated deposit. 15.The silver-alloy plated electrical contact of claim 14, wherein themetal complex forms about 0.3% to about 10% percent by weight of thecontent of the silver-alloy plated deposit.
 16. The silver-alloy platedelectrical contact of claim 14, wherein the metal complex is nickelcitrate-ammonia or cobalt citrate-ammonia.
 17. The silver-alloy platedelectrical contact of claim 14, wherein the silver complex is silverthiosulfate.
 18. The silver-alloy plated electrical contact of claim 14,wherein the silver complex is silver succinimide.
 19. The silver-alloyplated electrical contact of claim 14, wherein the silver-alloy platingbath has a pH of greater than 7.